Occludin regulates γδ intraepithelial lymphocyte migration in vivo

Intraepithelial lymphocytes (IELs) expressing the γδ T cell receptor promote mucosal homeostasis. To define the mechanisms by which they interact with enterocytes, jejunum of mice expressing GFP γδ T cells was imaged in vivo . At steady‐state, 32% of γδT cells are intraepithelial, but they exit this compartment with an average dwell time of ~6 min. This dynamic behavior allows each epithelial cell to interact with 3.5±0.2 γδIELs/hr. The tight junction protein occludin is expressed by γδIELs and concentrated at sites of γδIEL/epithelial contact. To assess the function of γδIEL occludin, mixed chimeras were generated by engrafting γδ T cell‐deficient marrow (80%), combined with either wildtype GFPγδ or occludin KO GFPγδ marrow (20%), into irradiated hosts. Occludin KO γδ T cells migrated into the epithelium inefficiently (13% vs. 41% for wildtype), and occludin KO γδIELs that crossed the basement membrane often remained subepithelial and rarely entered the lateral intercellular space. Occludin KO γδ T cells also migrated more slowly and interacted with fewer epithelial cells than wildtype γδ T cells (max speed 4.0±0.1 μm/min vs. 4.7±0.1μm/min, respectively; 1 epithelial cell/0.7±0.1 occludin KO γδIELs vs. 4.2±0.4 wildtype γδIELs/hr). Taken together, these data demonstrate that occludin is a critical regulator of γδIEL migration within the epithelium. Funding: NIH DK084859 (KLE), R01DK068271, R01DK061931 (JRT)